The invention relates to an apparatus and process for continuously producing a web from a thin sheet material which is corrugated at least in partial sections thereof and elastic at least in transverse direction. Moreover, the invention relates to an absorbent product comprising a corrugated web.
From examined German patent application DE 2011802 B2 laid open for public inspection an apparatus is known which, deals with the corrugation of a paper web. Due to the material properties of the paper to be processed, the shape of the guide bed of the known apparatus must be geometrically very complex and physically curved, which requires a high expenditure in production engineering and is thus disadvantageous.
From German patent DE 2945395 C2 a forming plate for a folding device of a cording machine is known consisting of a base plate and a plurality of folding ribs on the surface thereof, which ribs comprise parallel extending portions projecting beyond one edge of the base plate and portions extending radially or fan-shaped on the base plate. The folding ribs are separate blades which are releasably attached to the base plate and disposed in grooves formed in the base plate, each of which exhibits in a partial section a recess into which holding brackets engage which project from the lower edge of the blades. The known device does not enable a stabilization of corrugations. The corrugations formed are much rather pressed flat and fixed by sewing in a tube shape on the initial web.
A further device for forming longitudinal folds in a continuous web is described in German patent DE 3611134 C2. In this device, a very elastic paper which can be made almost plastically deformable by moistening, e.g., for cigarette filters, is slowly drawn into corrugations from the centre outwards between a large number of nested combing rollers. The embodiment shown of this very complex machine is only intended for forming corrugations in sections. Corrugations cannot be produced over the whole web due to the constant alternate web curvature.
Finally, German patent DE 2827495 C2 describes a device for transporting and combining a web of material in which the main aspect of the invention is the transportation of the web and simultaneous funnel-shaped tapering using a flow of air. It is not possible to obtain an exact corrugation of the folds with the known device.
The present invention is thus based on the object of providing apparatus and process for producing corrugated webs and absorbent articles which avoid the drawbacks of the prior art. This object is solved according to the invention by the apparatus, the process, and the absorbent articles. Further advantageous embodiments, aspects and details of the invention are evident from the dependent claims, the description and the drawings.
The apparatus of the invention comprises a guide bed into which fan-shaped grooves are cut, the depths of said grooves increasing preferably linearly to produce a corrugated cross-section of the desired dimension, into which holding-down devices dip from the opposite side according to the available height. The corrugated weds produced by means of the apparatus of the invention may have the same corrugation height over the entire web width of different corrugation heights if the guide bed is configured accordingly. It is self-evident to the person skilled in the art that the guide bed may also comprise one groove only if the desired corrugated web shall exhibit corresponding properties. In this case, only one holding-down device is required as well. The holding-down devices are preferably rod-shaped and preferably freely shiftable perpendicular to the guide bed at the end facing the inlet end of the guide bed as well as at the end facing the outlet end of the guide bed. The holding-down devices can be supported at both ends or may have one free unguided or unsupported end. It is advantageous for the holding-down devices to be of certain elasticity. Spring steel is a suitable material for the holding-down devices. The holding-down devices may be guided in at least one guide face extending perpendicular to the guide bed. If, in addition, the holding-down devices press the web against the guide bed through force-exerting means with a predetermined load, this will permit a certain adjusting effect for the continuous web which compensates for differences in tension in the material due to the formation of the folds not always being geometrically accurate. The predetermined force exerted on the holding-down devices can also be applied by a biasing of the holding-down devices. This renders additional force-exerting elements superfluous. Besides a round cross-section of the holding-down devices, which is particularly preferred, the holding-down devices may also have a triangular, rectangular, semicircular or trapezoidal cross-section.
It is of particular advantage for the free ends of the holding-down devices to be bent substantially parallel to each other or provided with corresponding shoulders which are received in bores of at least one guide element positioned at the end face. Furthermore, with respect to the direction of movement of the web, it is advantageous for all holding-down devices to be received forward and rearward, respectively, of the surface portion of the guide bed which comprises the grooves. Preferably, the holding-down devices are of round cross-section. The diameter may be, for example, from 0.1 to 5 mm, preferably 1 to 3 mm, in particular 2 mm. The distance between the grooves may be, for example, from 1 to 5 to 10 mm, preferably 2 to 4 mm.
The force-exerting means may, for example be a pressure plate which acts between the ends of the holding-down devices on same. The pressure plate, may additionally be provided with at least one spring member. Weights, compressed air, vacuum or magnets may also be used to exert a force. If magnets are used, permanent magnets as well as electromagnets are suitable which should be provided on the side of the guide bed opposite to the web to be formed. It is self-evident to the person skilled in the art that, when use is made of a magnet, the holding-down devices or an element acting on the holding-down devices, e.g., a contacting pressure plate, should exhibit ferromagnetic properties.
The corrugated webs of thin material produced by means of the apparatus of the invention or the process of the invention must be fixed after leaving the guide bed in order for the corrugations to remain permanently. One possibility to fix the corrugated web is to join it with a web material (backing web) or several web materials (backing webs). Another fixation possibility is to plastically deform the corrugated web permanently between stamping rollers. Furthermore, it is possible to fix the corrugation of the corrugated web in that a hardening agent is sprayed on. If a backing web is used to stabilize the corrugated web, the webs are preferably joined by a bonding agent, such as an adhesive. The joining, however, can also be effected by thermal treatment or ultrasonic welding.
According to a further embodiment, the guide-bed is provided, seen in cross-section, with different corrugation heights, the maximum corrugation height being usually formed in the center, the corrugation height decreasing towards the edges of the guide bed.
Furthermore, it is advantageous for the guide bed to be provided, seen transversely of the direction of movement of the material web, such that not all grooves start at the same height. It is particularly preferred for the grooves to start in the central portion of the guide bed, with grooves starting further downstream being arranged in the peripheral portions. Furthermore, it is desirable in certain embodiments for the guide bed to be so arranged as to be not provided with grooves over the entire width such that no grooves are provided in the central portion and/or the peripheral portions of the guide bed.
Finally, the apparatus of the invention may comprise a device with meshing rollers for stamping the produced corrugated web, said device with meshing rollers being provided downstream of the guide bed.
The corrugated web produced with the process of the invention and the apparatus of the invention can advantageously be used as component of an absorbent article for absorbing body fluids, such as a diaper, sanitary napkin or incontinence pads. Such an absorbent article usually comprises a liquid-impermeable cover sheet disposed away from the body in use, a liquid-permeable cover sheet disposed towards the body in use and an absorbent body disposed between said liquid-permeable and said liquid-impermeable cover sheet. The absorbent article of the invention is distinguished in that the liquid-permeable cover sheet and/or the absorbent body comprises at least in partial sections thereof corrugations (xe2x80x9cpleatingsxe2x80x9d). To this end, webs can be used which have been laid in folds by means of the process of the invention or the apparatus of the invention. The webs produced according to the invention are advantageous as compared to corrugated webs conventionally produced by means of stamping rollers in that they are of superior, wearing comfort and improved absorbing capacity, because the treated material is practically not compacted in the forming process.